Improvement in thermal efficiency of a steam turbine used in a thermal power station and the like has become an important task leading to efficient use of energy resources and a reduction in carbon dioxide (CO2) emission. Effectively converting given energy to mechanical work makes it possible to achieve the improvement in thermal efficiency of a steam turbine. To achieve this, reducing various internal losses is required.
The internal losses of the steam turbine includes a profile loss ascribable to a blade shape, turbine cascade losses based on a secondary flow loss of steam, a leakage loss of steam, a moisture loss of steam, and so on, passage part losses in passages other than a cascade, represented by a steam valve and a crossover pipe, turbine exhaust losses ascribable a turbine exhaust chamber, condenser internal losses occurring inside a condenser, and so on.
In a steam turbine including a turbine exhaust chamber of a downward exhaust type, the condenser internal loss out of these losses is classified into a pressure loss occurring in a connecting body part connecting the exhaust chamber of the steam turbine and a condenser main body part and a pressure loss occurring in the condenser main body part. Incidentally, the condenser main body part provides under the connecting body part and has a cooling pipe bundle group to condense steam.
The pressure loss in the connecting body part is a pressure loss in the steam flowing into the connecting body part. This pressure loss greatly depends on the shape of the connecting body part and the disposition of structures such as pipes. Generally, the pressure loss increases in proportion to the square of a flow velocity of the steam. Therefore, it is effective to reduce the flow velocity of the steam by increasing the size of the connecting body part in an allowable range. However, the increase of the size of the connecting body part is restricted by manufacturing cost, arrangement space of a building, and so on.
The connecting body part has a diffuser shape whose passage sectional area increases from its inlet toward its outlet. Inside the connecting body part, structural strength members are installed in addition to pipes such as neck heater pipes and turbine bypass pipes. In order to reduce the pressure loss in such a connecting body part, various studies have been made.
In the above-described connecting body part, the area and shape of the outlet are decided based on the arrangement structure of the cooling pipe bundle group which is required in the condenser main body part. Therefore, a spreading angle of spreading sidewalls of the connecting body part having the diffuser shape is decided by the required area and shape of the outlet of the connecting body part. Note that the spreading angle of the spreading sidewalls is an angle made by a vertical direction and an inner surface of each of the spreading sidewalls.
When the spreading angle of each of the spreading sidewalls becomes larger than a predetermined angle and accordingly the spreading sidewalls spread greatly, the steam flowing from the exhaust chamber of the steam turbine into the connecting body part separates in a passage on the spreading sidewall sides. Consequently, a pressure loss in the steam flowing into the connecting body part increases.